It is known that ferroelectric liquid crystal cells vibrate mechanically under the effect of ac fields. The vibrations are mainly due to the backflow and electroclinic effects. For small director ...oscillations the effect is mainly linear and goes with the frequency of the field. For larger oscillations higher harmonics appear too. We studied the practically interesting case when, due to rectangular excitation, the director switches fully between two stable positions. In the experiments bookshelf textures of (R)-MHPOBC and FLC6430 (from Hoffmann La Roche) were used. The accelerations of the cover plates due to the reversal of the field were detected in three orthogonal directions. The switches cause strong vibrations of the plates (lasting less than a millisecond,. acceleration ∼10m/s
2
). The vibration is largest at the SmCα*-Sm A phase transition indicating that the dominating effect is electroclinic in origin.
Achiral bent-shaped molecules may form chiral and polar smectic phases, due to a spontaneous tilt of the planes of the molecules. The lowest energy-state is racemic, and in the textures of the ground ...state usually fine fringes appear parallel to the smectic layers. Recently it was found that the formation of the fringes could be suppressed resulting in a uniform texture in the ground state. In this paper we show evidences for field induced tilted and horizontally zigzagging layer structures. We discuss properties of various layer structures and compare them to our experimental observations. Finally we give a qualitative explanation for the observed field-induced-uniform-racemic ground state.
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In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer have been synthesized and characterized. The distinct feature of the material is a very broad temperature range ...(about 50 oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.
Textiles are the most universal wearable interface. Textile functionality is being rapidly expanded to incorporate a wide range of new technologies. A new concept of combining liquid crystals with ...fibers effectively incorporates all of the functionality associated with liquid crystals. In this article we report how liquid crystals can be incorporated into fibers and fabrics that respond visually to temperature. Looking to the future, we can envision how these liquid‐crystal fabrics can be designed to respond to chemical and biological stimuli, signaling the presence of bacteria and viruses, and opening the potential for wearable medical sensors. In addition to the visual response, the fabrics can provide an electrical output, allowing them to be integrated into more sophisticated sensing systems.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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196.
Troublesome Alkoxythiophenes-Mesomorphic Behavior and Highly Efficient Synthesis Herbert, Mark R.; Sonpatki, Vaishali M.; Jakli, Antal ...
Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals,
20/7/1/, Volume:
365, Issue:
1
Journal Article, Conference Proceeding
The synthesis of a novel ferroelectric alkoxythiophene-containing liquid crystal is described together with the mesophase morphology of the material. The alkoxythiophene unit is introduced by a ...highly efficient ring closure of an appropriate γ-ketoester using Lawesson's reagent as the sulfurating agent. Our new cyclization methodology represents the most efficient synthetic pathway for the synthesis of this unit.
The “classical” challenge, raised by Emil Fischer as to why one monosaccharide arylhydrazone adopts a cyclic structure but another an acyclic structure, is answered here. The present comprehensive ...analysis of hexose and hexosamine arylhydrazones, based on 2D NMR spectroscopy and theoretical modeling, has established that the chain of hydrogen bonds needed for conformational selection can only be completed for d‐glucosamine derivatives. Thus, d‐glucosamine 4‐nitrophenylhydrazone exclusively adopts its cyclic form, but any configurational changes imply the formation of acyclic structures. In conclusion, three criteria dominate structure selection, namely 1) an amino function at the C‐2 position, 2) the “all‐equatorial” substitution mode of the pyranoid ring, and 3) an electron‐withdrawing group on the arylhydrazone are all needed to get the cyclic form only.
Cyclic or acyclic? Criteria determining the cyclic form of sugar arylhydrazones are listed: The buildup of a chain of hydrogen bonds, the key element of stability, was determined by high‐resolution NMR spectroscopy and QM data.
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A new banana-shaped achiral molecule, 1,3-phenylene bis4-(3-chloro-4-n-octyloxyphenyliminomethyl)benzoate (PBCOB) has been synthesized, and its ferroelectric properties and homeotropic alignment ...investigated. The presence of a lateral chloro-substituent in the Schiff 's base moiety prevents the regular stacking of molecules and results in lowering the transition temperature and the degree of crystallinity of the switchable banana phase. Their smectic mesophases, including a switchable banana phase B
7
, were characterized by differential scanning calorimetry, X-ray scattering and polarizing optical microscopy. Both the left- and right-handed helical domains are spontaneously formed upon cooling from the isotropic liquid to the switchable banana phase B
7
. By X-ray study, the smectic phases showed a layer spacing of 38.1 Å, compatible with the end-to-end distance of the molecule with a bent conformation. Significantly, the smectic B7 phase exhibited a periodicity of 292 Å that corresponds to a helical structure with periodicity about 7.5 times 38.1 Å. The spontaneous polarization for PBCOB is about 50 nCcm
-2
and shows a temperature dependence. The ferroelectric lyomesophase of PBCOB showed a ferroelectric electro-optical switching range extending more than 50°C, switchable at room temperature.
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